x86: Call early_res_to_bootmem one time

Simplify setup_node_mem: don't use bootmem from other node, instead
just find_e820_area in early_node_mem.

This keeps the boundary between early_res and boot mem more clear, and
lets us only call early_res_to_bootmem() one time instead of for all
nodes.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1265793639-15071-12-git-send-email-yinghai@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>